Modular breakwaters have been placed on sea bottoms in the vicinity of eroding shorelines to protect the shorelines from further erosion. However, it has been found that when such breakwaters are employed in areas where they are fully submerged, i.e., where the barrier or reef is placed in about seven to eight feet of water, concerns arise in assembling the breakwater and with toe scour adjacent the beachward (shoreward) face. As the slope of the sea bottom is increased, the tendency for shoreline erosion increases.
The problem of stabilizing the sea bottom adjacent the beachward (shoreward) face is exacerbated in man-made beaches, i.e., where sand has been pumped in to build-up the beach. These replenished beaches have relatively steep slopes in the area where they meet the natural sea bottom and have a very high tendency toward erosion. In these instances, scouring of the sea bottom adjacent the beachward (shoreward) toe of a submerged reef tends to diminish the erosion protection advantages of the reef and eventually reduces the stability of the artificial reef structure.
The prior art discloses modular breakwaters for minimizing or eliminating the scouring of sand adjacent to the beachward (shoreward) toe of the breakwater when the breakwater is submerged, in U.S. Pat. No. 5,238,326 and U.S. Pat. No. 5,102,257, the disclosures of which are incorporated herein by reference. U.S. Pat. No. 5,102,257 discloses that each module includes a base portion for supporting the module on a seabed, a gently sloping seaward face extending above the base portion, and a beachward (shoreward) face extending above the base portion. The beachward (shoreward) face includes a deflector for deflecting downwardly directed fluid currents away from the beachward (shoreward) face.
The seaward face also includes a recessed portion that forms a transversely extending concave surface adjacent to the top edge for directing fluid currents over the top edge and away from the beachward (shoreward) face. Accordingly, the concave surface in the seaward face also prevents currents from reaching the seabed adjacent to the beachward (shoreward) toe of the breakwater. This concave surface further reduces the velocity of the wave passing over the breakwater, thereby minimizing the velocity of currents that may reach the seabed adjacent to the beachward (shoreward) toe of the breakwater to greatly reduce the degree of beachward (shoreward) toe scour.
U.S. Pat. No. 5,238,326 discloses a system that works well to reduce wave energy and limit the offshore loss of sand during storms through the functioning of a "backwash flume" on the beachward (shoreward) side of the reef. During storms, a strong offshore or cross-current is present which would normally carry large amounts of sand offshore if the reef was not there. These currents are redirected upward or vertically when they encounter the beachward (shoreward) side of the reef and the "backwash flume." This vertical and sand laden current is redirected toward the beach when it encounters the next oncoming wave, thus the previously eroded beach sand is returned to the beach.
A problem may occur, particularly during storms, which has previously gone unanswered. Because the structures of various breakwaters, including ones with a "backwash flume," create a high velocity upward current from an otherwise offshore current, a vortex is sometimes formed on the beachward (shoreward) side of the reef during a storm. This vortex can scour sand away from the base of the reef along the beachward (shoreward) edge. It has been determined that, in general, the effect of this vortex only extends beachward (shoreward) of the reef a distance that is equal to the depth of the reef submergence with respect to a storm-elevated mean sea level. It has also been determined that the greatest amount of scour occurs at about one half this distance beachward (shoreward) of the reef.
Therefore, there is a need to provide a method and device for minimizing or eliminating scouring of sand adjacent to a modular breakwater's beachward (shoreward) toe due to beachward (shoreward) side vortexes when the breakwater is submerged.